1. Field of the Invention
The present invention is concerned with a two-web, cylinder printing press especially adapted for make ready and proofing of gravure cylinders or rollers, and for printing of high quality samples of finished products therefrom without the necessity of employing full-scale production equipment. More particularly, it is concerned with such a press which preferably includes a pair of shiftable impression rollers disposed proximal to the gravure roller, with means for shifting of the impression rollers alternately into a web-defining relationship with the gravure roller.
2. Description of the Prior Art
During high quality gravure printing operations, it is generally necessary to "make ready" and proof individual gravure cylinders or rollers which are received from an intaglio engraver. Such proofing and make ready generally involves printing with the roller and making necessary adjustments of color strengths, color hue, half tone solid printing relationships and other parameters, until the printer is satisfied that the roller in question meets established gravure printing standards. As can be appreciated, in some instances considerable effort must be expended in these preliminary operations for a given gravure roller, particularly where exacting printing criteria for the finished product have to be met.
In full-scale production runs using gravure equipment, normally a series (e.g. four or five) gravure printing stations are placed in an in-line relationship, and a web to be printed is passed in serial order through the respective gravure stations. In full-scale production equipment of this type where extensive footages of finished product are contemplated, make ready and proofing of the respective gravure rollers does not represent a significant economic drawback. That is to say, the printer can expend whatever quantity of web is required for insuring that all of the gravure rollers are properly operating to give desired printing results, inasmuch as the extent of the final production justifies the effort and expense. Thus, in full-scale production work, gravure roller make ready and proofing is accepted as a necessary preliminary to final printing.
In many cases however, the printer wishes to prepare samples of finished product of relatively small footages, e.g., one to five thousand lineal feet of printed web. In such cases the time and expense involved in gravure roller proofing becomes, proportionately speaking, very high. As will be readily understood, the time involved in make ready and proofing for a contemplated production run of one thousand lineal feet is the same as that required for a full-scale production run of many hundreds of thousands of feet. Accordingly, there is a real reluctance on the part of printers to interrupt full production schedules for the purpose of making small samples for salesmen or the like.
In response to the above problem, it has been known to employ a single station gravure press separate from full-scale production equipment for gravure roller make ready, proofing and printing of samples. Of course, such a scheme requires that each respective gravure roller be made ready and proofed, the required amount of finished printing therefrom accomplished, and the web rewound so that the operation can be repeated until completion. However, this procedure makes it extremely difficult to predict the number of lineal feet of finished printing for each color to run in order to achieve the final desired footage. For example, if during the make ready and proofing of the first gravure roller three thousand feet of web is expended as waste, and thereafter two thousand feet of web are printed as final product, there is no way of knowing whether the second or subsequent rollers can be made ready and proofed using the three thousand feet of web previously allotted in connection with the first roller. If more than three thousand feet is expended, a portion of the "finished" printing from the first roller is destroyed because the printing from the later roller is not up to standard. Thus, it has been the practice to err on the side of liberality in printing footages from the respective gravure rollers, in order to avoid not producing enough of the sample product; of course, this represents in many cases a significant waste of material.
It has also been suggested in the past to provide a completely separate make ready unit and proofing unit for gravure rollers. Such units have presented serious technical problems, however, primarily because of the fact that the printing conditions established during the make ready proofing phase are substantially different than those encountered during actual production. To give but one example, prior make ready and proofing units may operate at relatively slow speeds (e.g., one hundred fifty lineal feet per minute), whereas actual production runs are much faster, on the order of eight hundred feet per minute. Such a disparity can and often does represent a considerable difference in printing quality between the make ready and proofing phase, and full production. Hence, prior equipment of this type has not provided a real solution to the problems outlined above.